The mechanisms responsible for progressive myocardial dysfunction and remodeling of the cardiomyopathic, failing human heart are unknown. In general, these pathophysiologic mechanisms are likely to involve alterations in myocardial gene expression. Numerous recent studies have demonstrated that, in order to be meaningful, gene regulation and expression must be examined in the intact heart. The overall objective of this proposal is to investigate, in human subjects with myocardial failure from a dilated cardiomyopathy phenotype, the utility of gene expression profiling performed longitudinally as phenotype is dynamically modulated. We propose that "dynamic expression profiling" can identify gene categories as well as specific individual novel genes whose altered expression is potentially causally related to phenotypic improvement. The proposal tests one general hypothesis supported by preliminary data: that "improvement in the dilated cardiomyopathy phenotype is associated with an increase in metabolic category gene expression, and a decrease in expression within cytoskeletal, extracellular matrix, signal transduction, growth factors, transcription /translation/nucleotide synthesis, and cell cycle/apoptosis gene categories." Three Specific Aims in the proposal deal respectively with identification of categories of genes, individual genes, and kinetics of gene changes associated with phenotypic improvement in idiopathic dilated cardiomyopathy in response to 0-blocking agents. A 4th Aim compares mRNA quantitation between the Affymetrix GeneChip method and quantitative RT-PCR, for 38 genes. We have developed techniques to measure the expression of a large number of target genes in small quantities of human ventricular myocardium that can be obtained serially from the intact heart by right ventricular (RV) endomyocardial biopsy, using Affymetrix GeneChips and quantitative RT-QPCR. We have demonstrated that RT-QPCR used in a serial, longitudinal fashion is able to identify genes whose altered expression is a potential explanation for contractile dysfunction and chamber/myocyte remodeling. We have also demonstrated the utility of expression profiling in serial, longitudinal studies where phenotype is modulated by treatment, and we provide evidence that this approach is superior to "static" expression profiling performed within the context of a cross-sectional design.